英语翻译

英语翻译
3.4.Elucidating the possible oxidation of Sn2+ within Sn–HEDP and Sn–PEI-MP complexes
There were no changes in the 31P NMR spectra of samples of Sn(II) with HEDP or PEI-MP overnight,hence we can assume that no oxidation of Sn2+ occurred.Should this have been the case we would expect an increase in the ratio of intensities of the corresponding peaks,which would eventually approach the spectrum of the concerning Sn(IV)-complex at the respective pH.
In a study to understand the conditions needed for the oxidation of Sn2+ in the presence of HEDP,the complex was titrated with hydrogen-peroxide (30% H2O2).The metal to ligand ratio of 1:3 (pH 7.3) was chosen so as to limit any free/uncomplexed tin which would hydrolyze and precipitate out during the titrations.Throughout the investigation no precipitation was observed within the 1:3 mixtures,even over prolonged periods,which indicates that all tin was successfully complexed in solution and variations in the pH did not influence the Sn-ions directly–the [Sn–HEDP] complexes are stable enough to with-stand fluctuations in pH.Mixtures in which the metalion concentration was in excess,i.e.M:L > 1:1,exhibited immediate precipitation upon addition of NaOH.Precipitation eventually occurred in these solutions,even without any pH manipulation after a few hours – for both Sn2+ and Sn4+.
Oxidation of the tin in the [Sn(II)–HEDP]0 and the [Sn(II)–Sn(IV)–PEI-MP]4+ systems was induced by the addition of 30 μl ofH2O2,0.05 mol/L(Fig.9) and 0.010 mol/L(Fig.8) respectively.As expected,an increase in intensity of the resonances of the Sn(IV) complexes was observed in the case of HEDP,with a steady decrease in the intensity of the resonance at about 19 ppm,and for PEI-MP we observed the disappearance of the signal for the Sn(II) chelate,although only realizing some increase ( 35–45%) in intensity of the resonances for the Sn4+ complex.There is a increase in the free-ligand concentration ( 40– 55%),which could be due to the liberation of ligand that had been previously bound to Sn2+.The simultaneous increase in both amounts of [Sn(IV)–PEI-MP]2+ and free ligand after oxidation implies that the PEI-MP that had formerly been bound to Sn2+ is evenly distributed between Sn4+-bound and free ligand in solution.Furthermore,this would mean an increase in the free metal-ion concentration (i.e.at least half the tin-ions being released as reflected by the increase in free-ligand concentration).This is confirmed by the occurrence of slight precipitation upon completion of the oxidation driven by thereaction of Sn(IV) + 4OH-=Sn(OH)4(s).Approximately 1.6μmol of H2O2 per μmol of Sn2+ within the HEDP system,was needed to oxidize it in order to reach the equivalent complexation of Sn4+ at the same pH (Fig.9).For the [Sn(II)–PEI-MP]0 system 1.4μmol H2O2 per μmol Sn(II)–PEI-MP is needed.